Absence of parasitic nematodes in farmed, harvest quality Atlantic salmon (Salmo salar) in Norway – Results from a large scale survey

Abstract

A total of 4184 farmed Atlantic salmon (Salmo salar) were sampled and subsequently examined for nematodes between January 2014 and July 2015. The fish originated from 37 salmon farms along the coast of Norway and represented all salmon-producing counties. Samplings took place at processing facilities during regular slaughtering procedures and consisted of 3525 harvest quality salmon processed for human consumption and 659 discarded salmon including runts and fish discarded for other quality defects. Both viscera and musculature (fillets including belly flaps) of the salmon were screened by applying the UV-press method. No nematodes were found in any of the harvest quality salmon. The only nematode findings were from the viscera of three runts (loser fish) originating in southern or western Norwegian farms, and consisted of two Anisakis simplex (s.s.) larvae and three adults of the non-zoonotic species Hysterothylacium aduncum. The absence of nematodes in the harvest quality salmon relates most likely to the diet since healthy and normally developing salmon seem to rely exclusively on the heated and extruded dry-feed, which cannot contain any viable parasites. The runts, however, may feed opportunistically on whatever prey available in the cages, which apparently facilitates the transfer of nematodes. Thus, the present results suggest that the risk of any parasitic nematodes to occur in the flesh of farmed Norwegian salmon intended for human consumption is very low.